Systematic review with meta-analysis of the epidemiological evidence relating smoking to COPD, chronic bronchitis and emphysema

Table 8 Meta-regression analyses for current smoking of any product (or cigarettes if any product not available)^a

		COPD		CB
Characteristic	Level	Estimate^b (SE^c)	p^d	Estimate^b (SE^c)	p^d
Constant		+1.011 (0.156)		+1.335 (0.258)
Sex	Male	Base	< 0.05	Base	NS
	Female	-0.218 (0.045)		-0.097 (0.043)
	Combined	-0.007 (0.045)		+0.039 (0.082)
Continent	N America	Base	< 0.001	Base	< 0.001
	Europe	-0.347 (0.051)		-0.353 (0.052)
	Asia	-0.499 (0.079)		-0.493 (0.070)
	Other	-0.510 (0.081)		-0.144 (0.086)
Disease definition	Mortality	Base	< 0.001	Base	< 0.01
	Lung function (COPD) or symptoms (CB)	-0.435 (0.071)		-0.104 (0.232)
	Other	+0.049 (0.076)		-0.406 (0.232)
How asthma taken into account	Ignored	Base	< 0.001	Base	< 0.05
	Excluded	-0.334 (0.051)		+0.159 (0.076)
	Included in outcome definition	-0.721 (0.072)		No data
	Other	-0.055 (0.103)		+1.225 (0.237)
Smoking product	Any	Base	< 0.05	Base	NS
	Cigarettes (ignoring other products)	+0.255 (0.084)		-0.023 (0.136)
	Cigarettes only	+0.505 (0.099)		+0.410 (0.136)
Unexposed group	Never any product	Base	< 0.01	Base	NS
	Never cigarettes	-0.446 (0.077)		-0.127 (0.130)
RR adjusted for age	Yes	Base	NS	Base	< 0.01
	No	+0.076 (0.050)		+0.219 (0.039)
RR adjusted for factor other than age or sex	Yes	Base	NS	Base	NS
	No	+0.148 (0.057)		-0.007 (0.072)
Midpoint age	Per 10 years	+0.012 (0.002)	< 0.05	+0.003 (0.002)	NS

^a Based on the same data as for Table 7. See that table for further definition of RRs selected for analysis, and numbers of estimates of each characteristic level.
^b Estimates are of log RR. For a particular entry, the predicted RR for a given estimate is calculated by adding the constant to the values for each level applicable to the estimate (taking the value for the base level as zero) and taking the exponential of the result.
^c SE = standard error.
^d The p value is estimated from the drop in deviance from removing the characteristic from the model using an F-test. It is expressed as p < 0.001, p < 0.01, p < 0.05, p < 0.1 or NS (p ≥ 0.1).

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